illusion or domination ?

I run a dom build for gwen and take her everywhere with me. Is this a good idea or is illusion better ?

Domination works best i think.

Depends on the area.
Usually in caster heavy areas, domination will be the best choice because interruptions, debuff and hex eater vortex will be very usefull.
In melee heavy areas, an ineptitude/clumsiness spammer works better.

Domination magic is pretty solid in most areas, although in areas that are more heavy on physical attackers an illusion build can work wonders.

I have Gwen running a domination build, and Norgu running an illusion build. The game offers two mesmer heroes, so may as well customise them both to different lines of magic and switch the two in and out of the party as the environment calls for it

You can even make Gwen a tank :P

Hero AI is good at spreading degen, but can put backfire on melee. Heroes are good interrupters, but unable to prioritize the skills to interrupt. Illusion mesmer hero might behave more efficiently.